Various mounting arrangements have been developed for supporting sensitive instrumentation such a CMM, gyrocompasses, electron microscopes and other microprecision equipment or machines. Vibrations negatively affect the efficiency of these machines and hence mounting arrangements typically utilize vibration isolation systems to suppress vibrations and shocks at the site where the microprecision equipment is operated. The vibrations may be the result of: (1) the natural frequency of the surrounding structure; (2) the microprecision equipment itself, e.g., sudden movement of a measuring element in a CMM; and/or (3) vibrations resulting from environmental elements which enter the building where the microprecision equipment is operated. In the absence of vibration isolation equipment, vibrations will be transmitted to the precision equipment having both vertical and horizontal components.
Previously known conventional low frequency pneumatic isolation systems are designed with some form of elastically connected damper (e.g., an auxiliary reservoir with flow restrictors) applied in the vertical direction to improve the dynamics in settling and levelling, and provide some degree of isolation. Such a system is disclosed in U.S. Pat. No. 3,730,473. The effectiveness of such a system is significantly limited. First, the damping characteristics of the system cannot be readily modified, i.e., the damping characteristics are predetermined and are based on the size of the dual chambers (primary and auxiliary reservoirs) and the size of the restrictive passageways connecting the primary and auxiliary reservoirs. There is no simple and efficient means for adjusting the damping characteristics of the isolation system so that it can be used under varying operating conditions. This system is further limited in its ability to facilitate rapid settling of the precision equipment due to acceleration of a component (e.g., measuring or cutting element) of the precision equipment. This system is also limited in its ability to reduce the damping characteristic of the isolation system during the measuring or cutting stage of operation of the precision equipment thereby adversely impacting the isolation efficiency of the system. Moreover, this system is limited in its ability to provide smooth transition of the isolation system parameters between different stages of the cycle to avoid undesirable excitations at the point of measuring or cutting.